Track uses and defs during parsing.

Track uses and defs during parsing.

Replace two other, imperfect mechanisms for use-def tracking.

Use ValidationState_t::entry_points to track entry points.

Concentrate undefined-ID diagnostics in a single place.

Move validate_types.h content into validate.h due to increased
inter-dependency.

Track uses of all IDs: TYPE_ID, SCOPE_ID, ...

Also update some blurbs.

Fix entry-point accumulation and move it outside ProcessIds().

Remove validate_types.h from CMakeLists.txt.

Blurb for spvIsIdType.

Remove redundant diagnostics for undefined IDs.

Join "can not" and reformat.